Self-assembled, kinetically locked, Ru(II)-based metallomacrocycles: physical, structural, and modeling studies

By using a "complex as ligand approach," the metal-ion-templated self-assembly of heterometallic tetranuclear metallomacrocycles containing kinetically locked Ru(II) centers is described. Depending on the metal-ion template employed in the self-assembly process, the final macrocycle can be kinetically labile or inert. Electrochemical studies reveal that the kinetically inert macrocycles display reversible Ru(III/II) oxidation couples. The crystal structure of a kinetically inert Ru2Re2 macrocycles reveals a structurally complex palmate anion-binding pocket. Host-guest studies carried out with the same macrocyle in organic solvents reveals that the complex functions as a luminescent sensor for anions and that binding affinity and luminescent modulation is dependent on the structural nature and charge of the guest anion. Computational density functional theory (DFT) studies support the hypothesis that the luminescence of the macrocycle is from a 3MLCT state and further suggests that the observed guest-induced luminescence changes are most likely due to modulation of nonradiative decay processes.